This invention relates to a continuous motion orbital saw for transversely severing elongated multi-ply web material into shorter length products. More particularly, the invention relates to an orbital saw in which the cutting blade is mounted on a skew arm which rotates about an axis which is skewed relative to the path along which the elongated product is advanced. Compensation for the skew angle is accomplished by orbiting the blade in a planetary fashion so that the blade remains perpendicular to the path throughout the orbit. Grinding stones for sharpening the blade are positioned radially inwardly of the blade throughout the entire orbit.
A continuous motion saw is designed to cut a product in motion. Illustrative products are convolutely wound xe2x80x9clogsxe2x80x9d of bathroom tissue and kitchen toweling and bolts or continuous superposed plies of facial tissue.
There are a number of continuous motion saws which cut product that is in motion. The saw of U.S. Pat. No. Re. 30,598 uses a skew arm which rotates about an axis which is skewed with respect to the path along which the product is advanced. The disc blades for cutting the product are rotatably mounted on the skew arm so that the blades are perpendicular to the path. The supporting structures for the blades orbit in a planetary fashion about the skew axis to compensate for the skew angle so that the blades remain perpendicular to the path and make a square cut. The grinding stones for sharpening the blades also orbit with a planetary motion so that the grinding stones maintain the same relationship with the blades. However, the planetary motion of the grinders puts the grinders into completely reversing cyclic loading. The severe cyclic loading causes component fatigue and problems with grind quality as production speed increases.
In U.S. Pat. No. 5,315,907 the saw head is reciprocated parallel to the path of the product during its orbit. Although the grinding stones are mounted radially inwardly of the blade, all axes of motion are parallel.
U.S. Pat. Nos. 5,557,997, 5,924,346, and 6,123,002 describe a saw which uses a four bar linkage to orbit the blades rather than planetary motion. Eliminating planetary motion permits positioning the grinding stones radially inwardly of the blades. However, the four bar linkage is relatively complicated, and the preferred embodiment uses clutch means to maintain a constant forward index motion on internal components.
The invention uses planetary motion to compensate for the skew angle between the axis on which the skew arm rotates and the path of movement of the product. The planetary motion eliminates the need for clutch means since the components rotate at a continuous motion. In contrast to prior art saws with planetary motion, the grinding stones are positioned radially inwardly of the blade throughout the entirety of the blade orbit. Radially inwardly mounting the grinding stones is thereby accomplished without the complexity of the additional pivots and bars of the saws which use a four bar linkage.
One embodiment of the invention uses an angular differentiator to compensate for the skew angle. The angular differentiator is rotatably mounted on the skew arm and is driven in planetary fashion by a sun pulley and a planet pulley.
A second embodiment uses a self-aligning wobble bearing to compensate for the skew angle. The wobble bearing is mounted inside of the base for mounting the grinding stones.
A third embodiment uses intersecting axes in place of the angular differentiator. A kingshaft is rotatably mounted to the skew arm and extends perpendicularly to the skew axis. The base for mounting the grinding stones is pivotably mounted to the kingshaft parallel to the path of the product.